1. Field of the Invention
This invention relates to a receiver and a receiving-decoding method, and more particularly, is suitably applied to a receiver for receiving, for example, digital television broadcasts and outputting an obtained transport stream to an external device and also inputting a transport stream from an external device and decoding it.
2. Description of the Related Art
Digital television broadcasting has already started whereby a video signal is digitalized in accordance with the compressing encoding method such as the moving picture experts group phase 2 (MPEG 2) method and broadcasts it on ground waves or satellite waves.
In such digital television broadcasting, the audience needs a digital-broadcast receiver-decoder referred to as an integrated receiver decoder (IRD) which receives and decodes the ground waves and satellite waves.
In FIG. 1, 1 denotes a digital-broadcast receiver-decoder as a whole and an antenna 5 receives broadcast radio waves S1 and supplies it to a front end 10. The front end 10 demodulates the broadcast radio waves S1, generates a transport stream S10 composed of successive transport stream (TS) packets, and outputs the stream S10 to a decipherer 12. The decipherer 12 deciphers each enciphered TS packet in the case when each TS packet is enciphered and supplies it to a divider 15.
The divider 15 extracts desired TS packets from the transport stream S10, divides them into audio TS packets and video TS packets and supplies them to a decoder 16. The decoder 16 decodes the audio TS packets S15A and the video TS packets S15V supplied from the divider 15 in accordance with the MPEG 2 method, and outputs them as an audio signal S16A and a video signal S16V to an external device.
In this case, the front end 10 generates a byte clock S11 synchronous with the transport stream S10 when the transport stream S10 is generated by demodulating the broadcast waves S1 and outputs the byte clock S11 to the decipherer 12 and the divider 15. The byte clock S11 is a sync signal for synchronizing and transferring data. The front end 10, decipherer 12, and divider 15 operate in accordance with the byte clock S11 and thereby transfer TS packets composing the transport stream S10 synchronously with the byte clock S11.
In this kind of digital-broadcast receiver-decoder, it is possible to use a high-speed digital data interface such as an institute of electrical and electronics engineers (IEEE) 1394, output and store a transport stream obtained by receiving broadcast radio waves into a digital recorder such as an externally-set digital video tape recorder (VTR) via the digital data interface, and also input and decode the transport stream stored in the digital recorder via the digital data interface.
However, when a transport stream is inputted via the digital data interface, it is possible that the byte clock of a digital-broadcast receiver decoder (that is, the byte clock of a transport stream obtained by receiving broadcast waves) would not coincide with the byte clock of a transport stream inputted via the digital data interface, that is, data transfer rates would not coincide with each other. Moreover, when the byte clock of the transport stream inputted via the digital data interface is faster than that of the digital-broadcast receiver-decoder, a problem occurs that some of the TS packets are not transferred from the digital-broadcast receiver-decoder, which could lead into a decoding trouble.
Furthermore, there can be a case in which digital broadcasts are not received when inputting a transport stream from the digital data interface. In which case, the front end 10 cannot generate a byte clock, which can be an obstacle to the operation of the digital-broadcast receiver-decoder.
In view of the foregoing, an object of this invention is to provide a receiver and a receiving-decoding method having a simple configuration to receive digital broadcasts, and output the obtained transport stream to an external device, and also to decode a transport stream inputted from the external device.
The foregoing object and other objects of the invention have been achieved by the provision of a receiver which comprises: a receiving part for receiving and demodulating the digital broadcasts to output the first transport stream; a digital interface for receiving the second transport stream supplied from an external device; and a decoding processor for decoding the first transport stream received in the receiving part or the second transport stream received in the digital interface. The decoding processor changes clocks for transferring a transport stream depending on which of the first and second transport streams is being decoded.
Further, the present invention provides a receiving-decoding method for receiving digital broadcasts comprising the steps of: receiving and demodulating the digital broadcasts in the receiving part so as to output a first transport stream; receiving a second transport stream supplied from an external device in a digital interface; transferring to a decoding processor and decoding the first transport stream received in the receiving part or the second transport stream received in the digital interface; and changing clocks used for transferring the transport stream depending on which of the first and second transport streams is being decoded.
Because a clock corresponding to the transfer rate of a transport stream to be decoded is selected, it is possible to decode all data strings without fail.
Moreover, because the third clock used to transfer the second transport stream is generated by frequency-dividing a second clock necessary for the operation of the digital interface, the configuration is simplified without separately using a clock generating circuit.